Wireless device, a network node and methods therein for reporting channel state information (CSI) in a radio communications network

ABSTRACT

A method performed by a wireless device ( 121, 122 ) for determining Channel State Information, CSI, estimates to be transmitted in a CSI report for the wireless device ( 121, 122 ) to a network node ( 110 ) in a radio communications network ( 100 ) is provided. The wireless device ( 121, 122 ) receives a message comprising an indication to use CSI estimates corresponding to a determined period of time. In response to said message, the wireless device ( 121, 122 ) determines CSI estimates to be used in the CSI report to the network node ( 110 ) according to the received indication. A wireless device ( 121, 122 ) is also described. 
     A network node ( 110 ) and method therein for controlling CSI estimates transmitted by one or more wireless devices ( 121, 122 ) in CSI reports to the network node ( 110 ) in a radio communications network ( 100 ) are also provided.

This application is a continuation of U.S. patent application Ser. No.14/395,137, filed Oct. 17, 2014, which is a 35 U.S.C. § 371 nationalphase filing of International Application No. PCT/SE2014/050779, filedJun. 24, 2014, the disclosures of which are incorporated herein byreference in their entireties.

TECHNICAL FIELD

Embodiments herein relate to reporting Channel State Information, CSI,in a radio communications network. In particular, embodiments hereinrelate to a wireless device and a method therein for determining CSIestimates to be transmitted to a network node in a radio communicationsnetwork, and to a network node and a method therein for controlling CSIestimates transmitted by one or more wireless devices to the networknode in a radio communications network.

BACKGROUND

In a typical radio communications network, wireless devices, also knownas mobile stations, terminals, and/or User Equipments, UEs, communicatevia a Radio Access Network, RAN, with one or more core networks. The RANcovers a geographical area which is divided into cell areas, with eachcell area being served by a base station, e.g. a radio base station,RBS, or network node, which in some networks may also be called, forexample, a “NodeB”, “eNodeB” or “eNB”. A cell is a geographical areawhere radio coverage is provided by the radio base station at a basestation site or an antenna site in case the antenna and the radio basestation are not collocated. Each cell is identified by an identitywithin the local radio area, which is broadcast in the cell. Anotheridentity identifying the cell uniquely in the whole mobile network isalso broadcasted in the cell. One radio base station may have one ormore cells. The base stations communicate over the air interfaceoperating on radio frequencies with the user equipments within range ofthe base stations.

A Universal Mobile Telecommunications System, UMTS, is a thirdgeneration mobile communication system, which evolved from the secondgeneration, 2G, Global System for Mobile Communications, GSM. The UMTSterrestrial radio access network, UTRAN, is essentially a RAN usingwideband code division multiple access, WCDMA, and/or High Speed PacketAccess, HSPA, for user equipments. In a forum known as the ThirdGeneration Partnership Project, 3GPP, telecommunications supplierspropose and agree upon standards for third generation networks and UTRANspecifically, and investigate enhanced data rate and radio capacity. Insome versions of the RAN as e.g. in UMTS, several base stations may beconnected, e.g., by landlines or microwave, to a controller node, suchas a radio network controller, RNC, or a base station controller, BSC,which supervises and coordinates various activities of the plural basestations connected thereto. The RNCs are typically connected to one ormore core networks.

Specifications for the Evolved Packet System, EPS, have been completedwithin the 3^(rd) Generation Partnership Project, 3GPP, and this workcontinues in the coming 3GPP releases. The EPS comprises the EvolvedUniversal Terrestrial Radio Access Network, E-UTRAN, also known as theLong Term Evolution, LTE, radio access, and the Evolved Packet Core,EPC, also known as System Architecture Evolution, SAE, core network.E-UTRAN/LTE is a variant of a 3GPP radio access technology wherein theradio base station nodes are directly connected to the EPC core networkrather than to RNCs. In general, in E-UTRAN/LTE the functions of a RNCare distributed between the radio base stations nodes, e.g. eNodeBs inLTE, and the core network. As such, the Radio Access Network, RAN, of anEPS has an essentially “flat” architecture comprising radio base stationnodes without reporting to RNCs.

In a radio communications network, there is a need for a radio basestation to measure the channel conditions in order to know whattransmission parameters to use when transmitting to a wireless device.These parameters may comprise, e.g., modulation type, coding rate,transmission rank, and frequency allocation. This also applies to uplinkas well as downlink transmissions.

A scheduler that makes the decisions on the transmission parameters istypically located in the radio base station. Hence, the scheduler maymeasure channel properties of the uplink directly using known referencesignals that the wireless devices transmit. These measurements may thenform a basis for the uplink scheduling decisions that the radio basestation makes, which are then sent to the wireless devices via adownlink control channel.

However, for the downlink, the radio base station is unable to measureany channel parameters in a Frequency-Division Duplex, FDD, mode ofoperation. In a Time-Division Duplex, TDD, mode of operation, an uplinkmeasurement might be used in downlink. Due to calibration issues,however, these uplink measurements might not reflect the downlinkchannel used, and therefore, may not be well suited to be used asmeasurements of the downlink channel conditions.

Therefore, the radio base station must instead rely on information aboutthe channel conditions that the wireless devices may gather andsubsequently send back to the radio base station. This so-calledChannel-State Information, CSI, is obtained in the wireless devices bymeasuring on known reference symbols, such as, Channel-State InformationReference Symbols, CSI-RS, transmitted in the downlink (see e.g. 3GPP TS36.213 V11.4.0).

The CSI-RS resources are specifically configured for each wirelessdevice by using Radio Resource Control, RRC, signalling. A resource is agroup of resource elements in a certain subframe that occursperiodically, for instance every 20^(th) subframe. There is apossibility to configure both Non-Zero Power, NZP, CSI-RS resources andZero Power, ZP, CSI-RS resources. A ZP CSI-RS resource is simply anunused radio resource that can be matched to a NZP CSI-RS in an adjacentradio base station. This may then be used to improve the SINR for theCSI-RS measurements in the cell of the adjacent radio base station.However, the ZP CSI-RS resources may also be referred to or used asCSI-Interference Management, IM, resources. These are defined on thesame physical locations in the time/frequency grid as the CSI-RS, butwith zero power. These are intended to give a wireless device thepossibility to measure the power of interfering signals without havingit overlaid on top of a CSI-RS signal, which is usually much strongerthan any surrounding interference.

Each wireless device may be configured with one, three or four differentCSI processes. Each CSI process is associated with CSI-RS resources andCSI-IM resources. These CSI resources may be configured in the wirelessdevice by RRC signalling that may occur periodically, see e.g. 3GPP TS36.213 V11.4.0, 2013-09, Sections 7.2.5-7.2.6. For example, an RRCconfiguration message may be transmitted periodically every 5 ms, i.e.every 5th subframe. Alternatively, the RRC configuration message may besent in an aperiodic manner, or may be triggered in a control messagefrom the radio base station to a wireless device.

If only one CSI process is used, then it is common for the network tolet the CSI-IM reflect the interference from all other radio basestations, i.e. the cell of the serving radio base station uses a ZPCSI-RS that overlaps with the CSI-IM, but in other adjacent radio basestations, there is no ZP CSI-RS on these resources. In this way, thewireless device may measure the interference from adjacent cells usingmeasurements in the CSI-IM resource.

If more than one CSI processes are configured for the wireless device,then it is possible for the network to also configure a ZP CSI-RS in theadjacent radio base station that overlaps with a CSI-IM for the CSIprocess configured for the wireless device. In this way, the wirelessdevice may feedback accurate CSI estimates also for the case when thisadjacent cell is not transmitting. Hence, measurements to supportcoordinated scheduling between radio base stations is enabled with theuse of multiple CSI processes. One CSI process feeds back CSI estimatesfor the full interference case and the other CSI process feeds back CSIestimates for the case when an adjacent cell, preferably a stronginterfering cell, is muted. As mentioned above, up to four CSI processesmay be configured for a wireless device, thereby enabling feedback offour different transmission hypotheses.

If a CSI process is configured for a wireless device, the wirelessdevice may use an associated buffer or memory comprising one or multipleCSI measurements used to determine CSI estimates of the CSI process.However, how these CSI estimates are determined from the CSImeasurements are up to the implementation of the wireless device.

In LTE, the format of the CSI reports is specified in detail andcomprises CSI estimates in the form of Channel-Quality Indicator(s)(CQI), Rank Indicator (RI), and Precoding Matrix Indicator (PMI). Thequality and reliability of the CSI estimates, e.g. CQI, RI and PMI, arecrucial for the radio base station in order to make the best possiblescheduling decisions for the upcoming downlink transmissions.

SUMMARY

It is an object of embodiments herein to improve reporting of ChannelState Information, CSI, in a radio communications network.

According to a first aspect of embodiments herein, the object isachieved by a method performed by a wireless device for determining CSIestimates to be transmitted in a CSI report for at least one CSI processconfigured for the wireless device to a network node in a radiocommunications network. The wireless device receives a messagecomprising an indication to discard existing CSI estimates and/or anindication to use CSI estimates corresponding to a determined period oftime. Then, the wireless device determines CSI estimates to be used inthe CSI report to the network node according to the received indication.

According to a second aspect of embodiments herein, the object isachieved by a wireless device for determining CSI estimates to betransmitted in a CSI report for at least one CSI process configured forthe wireless device to a network node in a radio communications network.The wireless device is configured to receive a message comprising anindication to discard existing CSI estimates and/or an indication to useCSI estimates corresponding to a determined period of time. The wirelessdevice is also configured to determine CSI estimates to be used in theCSI report to the network node according to the received indication.

According to a third aspect of embodiments herein, the object isachieved by a method performed by a network node for controlling CSIestimates transmitted by one or more wireless devices in CSI reports ofat least one CSI process configured for the one or more wireless devicesto the network node in a radio communications network. The network nodedetermines that the CSI estimates from the one or more wireless devicesare no longer valid due to change in at least one transmissioncondition. Then, the network node transmits, to the one or more wirelessdevices, a message comprising an indication to discard existing CSIestimates and/or an indication to use CSI estimates corresponding to adetermined period of time.

According to a fourth aspect of embodiments herein, the object isachieved by a network node for controlling CSI estimates transmitted byone or more wireless devices in CSI reports of at least one CSI processconfigured for the one or more wireless devices to the network node in aradio communications network. The network node is configured todetermine that the CSI estimates from the one or more wireless devicesare no longer valid due to change in at least one transmissioncondition. Also, the network node is configured to transmit, to the oneor more wireless devices, a message comprising an indication to discardexisting CSI estimates and/or an indication to use CSI estimatescorresponding to a determined period of time.

According to a fifth aspect of embodiments herein, the object isachieved by a computer program, comprising instructions which, whenexecuted on at least one processor, cause the at least one processor tocarry out the method described above. According to a sixth aspect ofembodiments herein, the object is achieved by a carrier containing thecomputer program described above, wherein the carrier is one of anelectronic signal, optical signal, radio signal, or computer readablestorage medium.

By transmitting a message to discard existing CSI estimates and/or anindication to use CSI estimates corresponding to a determined period oftime, the network node is able to control the lifetime of the CSImeasurements in the wireless device. Thus, the network node is able toensure that CSI estimates reported back from the wireless device basedon these CSI measurements are not corrupted by CSI measurementsperformed previous to a change in a transmission condition to thewireless device, which improves the reliability of CSI estimates, whileat the same time reducing the number of RRC reconfiguration messageshaving to be transmitted, which improves the latency and mobility of thewireless device in the radio communications network.

Hence, the reporting of Channel State Information, CSI, in a radiocommunications network is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the embodiments will become readily apparentto those skilled in the art by the following detailed description ofexemplary embodiments thereof with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic block diagram illustrating embodiments of networknodes in a radio communications network,

FIG. 2 is a flowchart depicting embodiments of a method in a networknode,

FIG. 3 is a flowchart depicting embodiments of a method in a wirelessdevice,

FIG. 4 is a schematic block diagram depicting embodiments of a wirelessdevice.

FIG. 5 is a schematic block diagram depicting embodiments of a networknode.

DETAILED DESCRIPTION

The figures are schematic and simplified for clarity, and they merelyshow details which are essential to the understanding of the embodimentspresented herein, while other details have been left out. Throughout,the same reference numerals are used for identical or correspondingparts or steps.

FIG. 1 shows an example of a radio communications network 100 in whichembodiments herein may be implemented. Although illustrated in FIG. 1 asan LTE network, the radio communications network 100 may be any wirelesscommunication system, such as, LTE-Advanced, Wideband Code-DivisionMultiple Access (WCDMA), Global System for Mobilecommunications/Enhanced Data rate for GSM Evolution (GSM/EDGE),Worldwide Interoperability for Microwave Access (WiMax), Ultra MobileBroadband (UMB) or GSM network, or other 3GPP cellular network orsystem. The radio communications system 100 comprises the network node110.

The network node 110 may e.g. be an eNB, eNodeB, or a Home Node B, aHome eNode B, femto Base Station (BS), pico BS or any other network unitcapable to serve a wireless device in the radio communications system100. The network node 110 may also be e.g. a radio base station, a basestation controller, a network controller, a relay node, a repeater, anaccess point, a radio access point, a Remote Radio Unit (RRU) or aRemote Radio Head (RRH). Furthermore, the network node 110 comprises oneor more antennas for wireless radio communication with wireless deviceslocated within their coverage range; that is, the network node 110 mayuse one or more of its antennas to provide radio coverage within itscell 115.

A cell may be seen as a geographical area where radio coverage isprovided by radio base station equipment at a base station site or atremote locations by Remote Radio Units (RRU). The cell definition mayalso incorporate frequency bands and radio access technology used fortransmissions, which means that two different cells may cover the samegeographical area but using different frequency bands. Each cell isidentified by an identity within the local radio area, which isbroadcast in the cell. Another identity identifying each cell uniquelyin the whole radio communication network 100 may also be broadcasted inthe cell. The network node 110 communicates over the air or radiointerface operating on radio frequencies with the wireless deviceswithin range of the network node 110.

A first and a second wireless device 121, 122 are located within thecell 115. The wireless devices 121, 122 are configured to communicatewithin the radio communications network 100 via the network node 110over a radio link 131 when present in the cell 101 served by the networknode 110. The wireless devices 121, 122 may e.g. be any kind of wirelessdevice such as a mobile phone, a cellular phone, a Personal DigitalAssistant (PDA), a smart phone, a tablet, a sensor equipped with awireless device, Laptop-Mounted Equipment (LME) (e.g. USB),Laptop-Embedded Equipment (LEE), Machine-Type-Communication (MTC)device, a wireless device with D2D capability, Customer PremisesEquipment (CPE), etc.

Furthermore, although embodiments below are described with reference tothe scenario of FIG. 1, this scenario should not be construed aslimiting to the embodiments herein, but merely as an example made forillustrative purposes.

As part of developing the embodiments herein, it has been noticed thatthe LTE standard does not specify in detail how wireless devices shouldobtain and/or average CSI measurements from multiple time instants. Thismeans that wireless devices will measure over a time frame that isunknown to the network node and may combine several measurements in aproprietary way in order to create the CSI estimates of the CSI reportthat is then transmitted to the network node. It follows that the actualprocess of how the received CSI estimates are gathered, over which timeframe, and how they are calculated, by the wireless device is not knownto the network node. This makes it difficult for the network node toevaluate this information, and hence, make the best possible downlinkscheduling decisions. Hence, there is a need to improve the reliabilityof CSI estimates.

Furthermore, in emerging radio communications technology, the use ofarray antennas and beamforming is a key feature. Such radiocommunications technology enables a network node to transmit, andreceive, signal transmissions in specific spatial directions, known asbeams. Although this technology is still under development, it is likelythat individual transmit beams must somehow be possible to identify inthe wireless device. One solution to this would be to use beam-specificreference symbols, BRS, or CSI-RS resources that are associated with agiven beam or set of beams. Hence, the CSI-RS resources may bebeam-formed/precoded to reflect the channel when receiving data usingthe beam. The control of the transmit beam directions is handled in thenetwork node as part of the downlink scheduling. It should also be notedthat the direction of the used beam for the wireless device may changefrom Transmission-Time Interval, TTI, to TTI.

Therefore, in such radio communications networks, the problem of “stale”or outdated CSI estimates in the wireless device will become morepronounced, since which beam, or beams, that covers the wireless devicemay change completely between TTIs. A reason for this is that a beam maybe very narrow in angular beam-width, and the network node may need tochange the transmitting beam used for a wireless device very often whenthe wireless device moves through the cell. Also, changing beams willthen also require frequent RRC reconfigurations of the used CSI-RSresources for the wireless device since the CSI-RS are transmitted inbeams. Hence, another issue is that of frequent RRC reconfigurationsbeing needed to support beamformed CSI-RS together with mobility of thewireless device.

In accordance with embodiments described herein, these issues areaddressed by allowing the network to control the lifetime of CSImeasurements in the wireless device, by transmitting a message to thewireless device to discard existing CSI estimates and/or an indicationto use CSI estimates corresponding to a determined period of time, whenthere is a change in at least one transmission condition for thewireless device. In this way, the network node is able to ensure thatCSI estimates reported back from the wireless device are not corruptedby CSI measurements performed previous to the change. Hence, thereliability of CSI estimates in a radio communications network isimproved.

In addition, this will also reduce the need for transmitting RRCreconfiguration messages in the radio communications network in order toreconfigure the CSI-RS, since the CSI measurements may be reset usingthis type of message instead. This will improve latency and mobility ofthe wireless device in the radio communications network.

Hence, the reporting of CSI in a radio communications network is therebyimproved.

Example of embodiments of a method performed by a network node 110 forcontrolling Channel State Information, CSI, estimates transmitted by oneor more wireless devices 121, 122 in CSI reports of at least one CSIprocess configured for the one or more wireless devices 121, 122 to thenetwork node 110 in a radio communications network 100, will now bedescribed with reference to the flowchart depicted in FIG. 2.

FIG. 2 illustrates an example of actions or operations which may betaken by the network node 110. However, it should also be noted thatthese actions or operations may also be performed by a centralizednetwork node in the radio communications network 100, such as, e.g. acore network node, a radio network controller, a Radio ResourceManagement, RRM, server, an Operations Support System, OSS, node or thelike. The centralized network node may also be e.g. an eNB controllingdistributed Remote Radio Units, RRUs, via e.g. a Common Public RadioInterface, CPRI, or an eNB controlling radio heads over an activeDistributed Antenna System, DAS, network. The method may comprise thefollowing actions.

Action 201

The network node 110 first determines that the CSI estimates from theone or more wireless devices 121, 122 are no longer valid due to changein at least one transmission condition.

In some embodiments, the network node 110 may be configured forbeamforming transmissions to the one or more wireless devices 121, 122in the radio communications network 100. In this case, the change in theat least one transmission condition may be a change in transmittingbeams used in beamforming transmissions to the one or more wirelessdevices 121, 122. For example, this may be advantageous when the CSI-RSconfiguration has not changed and the one or more wireless devices 121,122 should keep measuring on the same CSI-RS, but the transmission beamscomprising the CSI-RS are pointing in new directions.

Alternatively, the change in the at least one transmission condition isa change in the traffic situation in the cell 115 in which the one ormore wireless devices 121, 122 are located. For example, the networknode 110 may become aware of, or determine, that the traffic situationfor wireless devices in the current cell 115, or other cells adjacent tothe cell 115, has changed, thus requiring new CSI measurement to beperformed in the one or more wireless device 121, 122 in order for theCSI estimates in the CSI report to properly reflect the current channelconditions.

Another option is that the change in the at least one transmissioncondition is a change in the determined period of time. This may, forexample, be that the desired periodicity has changed in the network node110 for the CSI measurements performed in the one or more wirelessdevices 121, 122.

Action 202

Following the determination in Action 201, the network node 110transmits, to the one or more wireless devices 121, 122, a messagecomprising an indication to discard existing CSI estimates and/or anindication to use CSI estimates corresponding to a determined period oftime. This means, for example, that the network node 110 may transmit amessage to the one or more wireless device 121 to flush CSI bufferscorresponding to one or more particular CSI processes. Advantageously,this may be performed without the having to transmit RRC reconfigurationmessages to the one or more wireless devices 121, 122 in the radiocommunications network 100.

The message may, for example, comprise the numbers or identities of theone or more CSI process whose CSI buffers should be flushed. However,the message may also, for example, also explicitly indicate to the oneor more wireless devices 121, 122 to flush and restart all CSImeasurements, so the CSI buffers of all CSI processes are flushed.

Consequently, the network node 110 may thus cause the one or morewireless device 121 to, for example, stop accumulating and averaging CSImeasurements to form the CSI estimates for one or more CSI processes,and begin over again with empty CSI buffers to collect new CSImeasurements forming new CSI estimates for the one or more CSIprocesses.

In some embodiments, the message may comprise an indication to discardCSI estimates determined via at least CSI-Reference Symbol, CSI-RS,resources associated with the at least one CSI process. Thisadvantageously enables the network node 110 to cause the one or morewireless devices 121, 122 to flush only the CSI-RS buffers of the atleast one CSI process, i.e. CSI buffers comprising CSI measurementsdetermined via the CSI-RS resources or Non Zero Power, NZP, CSI-RSresources. Thus, while these CSI-RS buffers are reset, the one or morewireless devices 121, 122 may keep the content of the CSI-IM buffers,i.e. CSI buffers comprising CSI measurements determined via the CSI-IMresources or Zero Power, NZP, CSI-RS resources.

Alternatively, in some embodiments, the message may comprise anindication to discard CSI estimates determined via at leastCSI-Interference Measurement, CSI-IM, resources associated with the atleast one CSI process. This advantageously enables the network node 110to cause the one or more wireless devices 121, 122 to flush only theCSI-IM buffers of the at least one CSI process.

According to some embodiments, the message may be transmitted as part ofa Radio Resource Control, RRC, reconfiguration message to the at leastone wireless device 121 in order to reconfigure the at least one CSIprocess. For example, as soon as a CSI process is reconfigured, which istypically controlled by higher-layer signalling from the network node110, the network node 110 may transmit the message. This may, forexample, be performed when reconfiguring one particular CSI process, butflushing the CSI buffers of at least one other CSI process.Alternatively, the network node 110 may also include the message as amandatory part of the reconfiguration message.

The message may also be transmitted to the at least one wireless device121 as part of a broadcasted reconfiguration message in order toreconfigure the at least one CSI process. This means that the messagemay, for example, be broadcasted to some or all wireless devices 121,122 in a cell, e.g. cell 115. This would result in a reduced signallingoverhead compared to messages specifically transmitted to each wirelessdevice 121. Such a broadcasted message for some or all wireless devices121, 122 to restart their CSI measurements may advantageously beperformed by the network node 110 when a large reconfiguration oftransmitted CSI-RS resources is performed.

Another option is that the message may be transmitted as part ofDownlink Control Information, DCI, to the at least one wireless device121.

It also should be noted that the message may, for example, be a downlinkmessage that is sent via a downlink control channel, such as, e.g. aPhysical Downlink Control CHannel, PDCCH, or an enhanced PDCCH, ePDCCH.The downlink message may also be transmitted by Radio Resource Control,RRC, signalling. Thus, the message transmitted by the network node 110may also be referred to a control message or control signalling message.

In some embodiments, the message may comprise an indication to use CSIestimates corresponding to a determined period of time. This means thatthe network node 110 may control the time frame during which theCSI-process has collected CSI measurements used in determining the CSIestimates. For example, the message may detail for how long a CSImeasurement is to be considered “fresh” or valid before it must bediscarded. This type of message may be directed by the network node 110towards a specific wireless device 121 or broadcasted to some or allwireless devices 121, 122. The message may comprise, for example, theapplicable CSI-process number or identity, and may specify, e.g. via anindex, an indicator or by some appropriate unit of time, for how longCSI measurements may be used by a wireless device 121 for calculating ordetermining the CSI estimates.

According to one example, the network node 110 may also force a wirelessdevice 121 to report CSI estimates without performing an averaging ofthe CSI measurements, so that the wireless device 121 only reports CSIestimates corresponding to the CSI measurements measured from a singletime instant. The network node 110 may then, for example, perform itsown averaging of the reported CSI estimates from several selected CSImeasurement time instants.

Furthermore, in some embodiments, the message may comprise an indicationof a determined period of time. The indication of the determined periodof time may, for example, be an n-bit field for some value of n thatcovers a specified range of time values, e.g. in milliseconds or someother suitable time scale. The indication of the determined period oftime may also be an index or indicator forming part of a range ofindices or indicators which relate to a table in the wireless devices121, 122 correlating the indices or indicators to specific time values.

Action 203

In this optional action, the network node 110 may receive a confirmationof the determined period of time from the one or more wireless devices121, 122. This may be performed in case the network node 110 hastransmitted a message comprising an indication to use CSI estimatescorresponding to a determined period of time in Action 202. Theconfirmation may, for example, be received as a separate message or aspart of the CSI report.

This advantageously enables the network node 110 to be notified that thewireless device 121 has received the message correctly. For example, inthe case of a message directed by the network node 110 to a specificwireless device 121 for flushing CSI buffers of one or more CSIprocesses, the network node 110 will be notified that this message hasbeen correctly received by the specific wireless device 121. Also, forexample, in the case of a broadcasted message directed by the networknode 110 to some or all wireless devices 121, 122 in a cell 115 forflushing CSI buffers of one or more CSI processes, the network node 110will be notified of which of the some or all wireless devices 121, 122in the cell 115 have correctly received the message. It also followsthat the network node 110 is thus notified whether the message wascorrectly decoded by the wireless devices 121, 122, that is, that themessage was decoded early enough to measure for as long a time frame asrequested in the indication before reporting the CSI estimates in theCSI reports.

It should be noted that an advantage of the embodiments described aboveis that an improved control in the network node 110 of the validity ofthe CSI estimates in received CSI reports is provided.

Furthermore, stale or obsolete CSI measurements may, according to theembodiments described herein, be discarded or purged by the network node110 without having to transmit RRC reconfiguration messages, i.e.minimizing RRC signalling. Further advantages comprise the fact that thetime frame during which the CSI measurement has been obtained may beknown in the network node 110, and the precise ways in which the CSIestimates in the CSI reports have been determined or calculated may beknown in the network node 110. These advantages also provide the networknode 110 with an improved basis when making downlink schedulingdecisions.

Example of embodiments of a method performed by a wireless device 121for determining Channel State Information, CSI, estimates to betransmitted in a CSI report for at least one CSI process configured forthe wireless device 121 to a network node 110 in a radio communicationsnetwork 100, will now be described with reference to the flowchartdepicted in FIG. 3. FIG. 3 is an illustrated example of actions oroperations which may be taken by the wireless device 121. The method maycomprise the following actions.

Action 301

The wireless device 121 receives a message comprising an indication todiscard existing CSI estimates and/or an indication to use CSI estimatescorresponding to a determined period of time.

According to some embodiments, the message may be received as part of aRadio Resource Control, RRC, reconfiguration message to the wirelessdevice 121 in order to reconfigure the at least one CSI process. Themessage may also be received as part of a broadcasted reconfigurationmessage in order to reconfigure the at least one CSI process. Anotheroption is that the message may be received as part of Downlink ControlInformation, DCI, to the wireless device 121.

Action 302

After receiving the message in Action 301, the wireless device 121determines CSI estimates to be used in the CSI report to the networknode 110 according to the received indication.

The wireless device 121 is continuously buffering CSI measurements basedon at least CSI-RS resources, and potentially also CSI-IM resources, todetermine or compute CSI estimates for a given CSI process, such as, forexample, Channel-Quality Indicator(s) (CQI), Rank Indicator (RI), andPrecoding Matrix Indicator (PMI). So, for example, based on theindication in the message, the wireless device 121 may stop accumulatingand averaging its current CSI measurements, and begin over again with anempty CSI buffer to collect new CSI measurements for determining CSIestimates. Thus, in some embodiments, when an indication to discardexisting CSI estimates is received, the wireless device 121 may discardall existing CSI estimates and determine new CSI estimates. This maycomprise discarding both existing CSI estimates determined via CSI-RSresources associated with the at least one CSI process, i.e. the CSI-RSbuffer(s), and existing CSI estimates determined via CSI-IM resourcesassociated with the at least one CSI process, i.e. CSI-IM buffer(s).

Alternatively, when the indication in the message indicates to discardCSI estimates determined via at least CSI-RS resources associated withthe at least one CSI process, the wireless device 121 may discardexisting CSI estimates determined via at least CSI-RS resourcesassociated with the at least one CSI process. Here, the wireless device121 may discard only the existing CSI estimates determined via CSI-RSresources associated with the at least one CSI process, i.e. flush thecontent of the CSI-RS buffer(s), and determine new CSI estimates.

Furthermore, when the indication in the message indicates to discard CSIestimates determined via at least CSI-IM resources associated with theat least one CSI process, the wireless device 121 may discard existingCSI estimates determined via at least CSI-IM resources associated withthe at least one CSI process. Here, the wireless device 121 may discardonly the existing CSI estimates determined via CSI-IM resourcesassociated with the at least one CSI process, i.e. flush the content ofthe CSI-IM buffer(s), and determine new CSI estimates.

In some embodiments, when the indication in the message indicates to useCSI estimates corresponding to a determined period of time, the wirelessdevice 121 may, according to some embodiments, discard existing CSIestimates which do not correspond to the determined period of time anddetermine new CSI estimates which correspond to the determined period oftime. The indication of the determined period of time may, for example,be an n-bit field for some value of n that covers a specified range oftime values, e.g. in milliseconds or some other suitable time scale. Theindication of the determined period of time may also be an index orindicator forming part of a range of indices or indicators which relateto a table in the wireless devices 121 correlating the indices orindicators to specific time values.

It should be noted that the indication of the determined period of timemay also indicate that both existing CSI measurements and new CSImeasurements made within the determined period of time is to be used bythe wireless device 121 when determining the CSI estimates, or that onlynew CSI measurements made within the determined period of time is to beused by the wireless device 121 when determining the CSI estimates.

Action 303

In this optional action, the wireless device 121 may transmit aconfirmation of the determined period of time to the network node 110.This may be performed in case the wireless device 121 has received amessage comprising an indication to use CSI estimates corresponding to adetermined period of time in Action 301. The confirmation may, forexample, be sent as a separate message or as part of the CSI report tothe network node 110.

To perform the method actions in the first wireless device 121 fordetermining CSI estimates to be transmitted in a CSI report for at leastone CSI process configured for the wireless device 121 to a network node110 in the radio communications network 100, the first wireless device121 may comprise the following arrangement depicted in FIG. 4. FIG. 4shows a schematic block diagram of embodiments of the first wirelessdevice 121. In some embodiments, the first wireless device 121 maycomprise a transceiving module 401 and a determining module 402. In someembodiments, the first wireless device 121 may comprise a processingcircuitry 410, which may also be referred to as processing module,processing unit or processor. The processing circuitry 410 may compriseone or more of the transceiving module 401 and the determining module402, and/or itself perform the function thereof described below.

The first wireless device 121 is configured to, e.g. by means of thetransceiving module 401, receive a message comprising an indication todiscard existing CSI estimates and/or an indication to use CSI estimatescorresponding to a determined period of time. Also, the first wirelessdevice 121 is configured to, e.g. by means of the determining module402, determine CSI estimates to be used in the CSI report to the networknode 110 according to the received indication.

In some embodiments, the first wireless device 121/the determiningmodule 402 may be configured to discard all existing CSI estimates anddetermine new CSI estimates when an indication to discard existing CSIestimates is received. In some embodiments, the first wireless device121/the determining module 402 may be configured to discard existing CSIestimates determined via at least CSI-RS resources associated with theat least one CSI process when the indication in the message indicates todiscard CSI estimates determined via at least CSI-RS resourcesassociated with the at least one CSI process. In some embodiments, thefirst wireless device 121/the determining module 402 may be configuredto discard existing CSI estimates determined via at least CSI-IMresources associated with the at least one CSI process when theindication in the message indicates to discard CSI estimates determinedvia at least CSI-IM resources associated with the at least one CSIprocess.

In some embodiments, the first wireless device 121/the transceivingmodule 401 may be configured to receive the message as part of a RadioResource Control, RRC, reconfiguration message to reconfigure the atleast one CSI process, as part of a broadcasted reconfiguration messageto reconfigure the at least one CSI process, or as part of DownlinkControl Information, DCI.

In some embodiments, the first wireless device 121/the determiningmodule 402 may be configured to discard existing CSI estimates which donot correspond to the determined period of time and determine new CSIestimates which correspond to the determined period of time when theindication in the message indicates to use CSI estimates correspondingto a determined period of time. In this case, the first wireless device121/the determining module 402 may further be configured to, transmit aconfirmation of the determined period of time to the network node 110.

The wireless device 121 in FIG. 4 may also be described as a wirelessdevice 121 for determining CSI estimates to be transmitted in a CSIreport for at least one CSI process configured for the wireless device121 to a network node 110 in a radio communications network 100,comprising a transceiving module 401 for receiving a message comprisingan indication to discard existing CSI estimates and/or an indication touse CSI estimates corresponding to a determined period of time, and adetermining module 402 for determining CSI estimates to be used in theCSI report to the network node 110 according to the received indication.Also, the transceiving module 401 may also transmit a confirmation ofthe determined period of time to the network node 110.

The embodiments for determining CSI estimates to be transmitted in theCSI report for at least one CSI process configured for the wirelessdevice 121 may be implemented through one or more processors, such as,e.g. the processing circuitry 410 in the first wireless device 121depicted in FIG. 4, together with computer program code for performingthe functions and actions of the embodiments herein. The program codementioned above may also be provided as a computer program product, forinstance in the form of a data carrier carrying computer program code orcode means for performing the embodiments herein when being loaded intothe processing circuitry 410 in the first wireless device 121. Thecomputer program code may e.g. be provided as pure program code in thefirst wireless device 121 or on a server and downloaded to the firstwireless device 121. The carrier may be one of an electronic signal,optical signal, radio signal, or computer readable storage medium, suchas, e.g. electronic memories like a RAM, a ROM, a Flash memory, amagnetic tape, a CD-ROM, a DVD, a Blueray disc, etc.

The first wireless device 121 may further comprise a memory 420, whichmay be referred to or comprise one or more memory modules or units. Thememory 420 may be arranged to be used to store executable instructionsand data to perform the methods described herein when being executed inthe first wireless device 121. Those skilled in the art will alsoappreciate that the processing circuitry 410 and the memory 420described above may refer to a combination of analog and digitalcircuits, and/or one or more processors configured with software and/orfirmware, e.g. stored in the memory 420, that when executed by the oneor more processors such as the processing circuitry 410 perform themethod as described above. The processing circuitry 410 and the memory420 may also be referred to as processing means. One or more of theseprocessors, as well as the other digital hardware, may be included in asingle application-specific integrated circuit (ASIC), or severalprocessors and various digital hardware may be distributed among severalseparate components, whether individually packaged or assembled into asystem-on-a-chip (SoC).

From the above it may be seen that some embodiments may comprise acomputer program product, comprising instructions which, when executedon at least one processor, e.g. the processing circuitry 410 or modules401-402, cause the at least one processor to carry out the method fordetermining CSI estimates to be transmitted in a CSI report for at leastone CSI process configured for the wireless device 121. Also, someembodiments may, as described above, further comprise a carriercontaining said computer program, wherein the carrier is one of anelectronic signal, optical signal, radio signal, or computer readablestorage medium.

To perform the method actions in the network node 110 for controllingCSI estimates transmitted by one or more wireless devices 121, 122 inCSI reports of at least one CSI process configured for the one or morewireless devices 121, 122 to the network node 110 in a radiocommunications network 100, the network node 110 may comprise thefollowing arrangement depicted in FIG. 5.

FIG. 5 shows a schematic block diagram of embodiments of the networknode 110. In some embodiments, the network node 110 may comprise adetermining module 501 and a transceiving module 502. In someembodiments, the network node 110 may comprise a processing circuitry510, which may also be referred to as processing module, processing unitor processor. The processing circuitry 510 may comprise one or more ofthe determining module 501 and the transceiving module 502, and/orperform the function thereof described below.

The network node 110 is configured to, e.g. by means of the determiningmodule 501, determine that the CSI estimates from the one or morewireless devices 121, 122 are no longer valid due to change in at leastone transmission condition. Also, the network node 110 is configured to,e.g. by means of the transceiving module 502, transmit, to the one ormore wireless devices 121, 122, a message comprising an indication todiscard existing CSI estimates and/or an indication to use CSI estimatescorresponding to a determined period of time.

In some embodiments, wherein the network node 110/transceiving module502 is configured for beamforming transmissions to the one or morewireless devices 121, 122 in the radio communications network 100, thechange in the at least one transmission condition may be a change intransmitting beams used in beamforming transmissions to the one or morewireless devices 121, 122. In some embodiments, the change in the atleast one transmission condition may be a change in the trafficsituation in the cell 115 in which the one or more wireless devices 121,122 is located. In some embodiments, the change in the at least onetransmission condition may be a change in the determined period of time.

In some embodiments, the message may comprise an indication to discardCSI estimates determined via at least CSI-RS resources associated withthe at least one CSI process. In some embodiments, the message maycomprise an indication to discard CSI estimates determined via at leastCSI-IM resources associated with the at least one CSI process.

In some embodiments, the network node 110/the transceiving module 502may be configured to transmit the message as part of a Radio ResourceControl, RRC, reconfiguration message to reconfigure the at least oneCSI process, as part of a broadcasted reconfiguration message toreconfigure the at least one CSI process, or as part of Downlink ControlInformation, DCI.

In some embodiments, the message may comprise an indication to use CSIestimates corresponding to a determined period of time. In someembodiments, the message may comprise an indication of a determinedperiod of time. In some embodiments, the network node 110/thetransceiving module 502 may be configured to receive a confirmation ofthe determined period of time from the one or more wireless devices 121,122.

The network node 110 in FIG. 5 may also be described as a network node110 for controlling CSI estimates transmitted by one or more wirelessdevices 121, 122 in CSI reports of at least one CSI process configuredfor the one or more wireless devices 121, 122 to the network node 110 ina radio communications network 100, comprising a determining module 501for determining that the CSI estimates from the one or more wirelessdevices 121, 122 are no longer valid due to change in at least onetransmission condition, and a transceiving module 502 for transmitting,to the one or more wireless devices 121, 122, a message comprising anindication to discard existing CSI estimates and/or an indication to useCSI estimates corresponding to a determined period of time.

The embodiments for controlling CSI estimates transmitted by one or morewireless devices 121, 122 in CSI reports may be implemented through oneor more processors, such as, e.g. the processing circuitry 510 in thenetwork node 110 depicted in FIG. 5, together with computer program codefor performing the functions and actions of the embodiments herein. Theprogram code mentioned above may also be provided as a computer programproduct, for instance in the form of a data carrier carrying computerprogram code or code means for performing the embodiments herein whenbeing loaded into the processing circuitry 510 in the network node 110.The computer program code may e.g. be provided as pure program code inthe network node 110 or on a server and downloaded to the network node110. The carrier may be one of an electronic signal, optical signal,radio signal, or computer readable storage medium, such as, e.g.electronic memories like a RAM, a ROM, a Flash memory, a magnetic tape,a CD-ROM, a DVD, a Blueray disc, etc.

Thus, the network node 110 may further comprise a memory 520, which maybe referred to or comprise one or more memory modules or units. Thememory 520 may be arranged to be used to store executable instructionsand data to perform the methods described herein when being executed inthe network node 110, the processing circuitry 510 and/or modules501-502. Those skilled in the art will also appreciate that theprocessing circuitry 510 and the memory 520 described above may refer toa combination of analog and digital circuits, and/or one or moreprocessors configured with software and/or firmware, e.g. stored in thememory 520, that when executed by the one or more processors, such as,the processing circuitry 510 and/or modules 501-502, cause the one ormore processors to perform the method as described above. The processingcircuitry 510 and the memory 520 may also be referred to as processingmeans. One or more of these processors, as well as the other digitalhardware, may be included in a single application-specific integratedcircuit (ASIC), or several processors and various digital hardware maybe distributed among several separate components, whether individuallypackaged or assembled into a system-on-a-chip (SoC).

From the above it may be seen that some embodiments may comprise acomputer program product, comprising instructions which, when executedon at least one processor, e.g. the processing circuitry 510 or modules501-502, cause the at least one processor to carry out the method forcontrolling CSI estimates transmitted by one or more wireless devices121, 122 in CSI reports. Also, some embodiments may further comprise acarrier containing said computer program product, wherein the carrier isone of an electronic signal, optical signal, radio signal, or computerreadable storage medium.

The terminology used in the detailed description of the particularembodiments illustrated in the accompanying drawings is not intended tobe limiting of the described methods, wireless device 121 and thenetwork node 110, which instead should be construed in view of theenclosed claims.

As used herein, the term “and/or” comprises any and all combinations ofone or more of the associated listed items.

Further, as used herein, the common abbreviation “e.g.”, which derivesfrom the Latin phrase “exempli gratia,” may be used to introduce orspecify a general example or examples of a previously mentioned item,and is not intended to be limiting of such item. If used herein, thecommon abbreviation “i.e.”, which derives from the Latin phrase “idest,” may be used to specify a particular item from a more generalrecitation. The common abbreviation “etc.”, which derives from the Latinexpression “et cetera” meaning “and other things” or “and so on” mayhave been used herein to indicate that further features, similar to theones that have just been enumerated, exist.

As used herein, the singular forms “a”, “an” and “the” are intended tocomprise also the plural forms as well, unless expressly statedotherwise. It will be further understood that the terms “includes,”“comprises,” “including” and/or “comprising,” when used in thisspecification, specify the presence of stated features, actions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,actions, integers, steps, operations, elements, components, and/orgroups thereof.

Unless otherwise defined, all terms comprising technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which the described embodiments belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The embodiments herein are not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be construed aslimiting.

ABBREVIATIONS

CQI Channel-Quality Indicator

CSI Channel-State Information

CSI-IM Channel-State Information—Interference Measurement

CSI-RS Channel-State Information—Reference Signal

DL Downlink

DMRS Demodulation Reference Signals

eNB evolved NodeB

ePDCCH enhanced Physical Downlink Control Channel

FDD Frequency-Division Duplex

LTE Long-Term Evolution

PDCCH Physical Downlink Control Channel

PMI Precoding Matrix Indicator

RI Rank Indicator

RRC Radio Resource Control

TDD Time-Division Duplex

TTI Transmission-Time Interval

UE User Equipment

UL Uplink

ZP Zero Power

The invention claimed is:
 1. A method performed by a User Equipment, UE,for determining Channel State Information, CSI, estimates to betransmitted in a CSI report to a base station in a radio communicationsnetwork, the method comprising: receiving a message comprising anindication to use CSI estimates that are based on a CSI measurement atonly a single time instant on a Channel State Information ReferenceSymbols, CSI-RS, resource configured for the UE, and that are furtherbased on a CSI measurement on a Channel State Information InterferenceMeasurement, CSI-IM, resource at only the single time instant;discarding existing CSI estimates when there is a change in at least onetransmission condition for the UE; determining the CSI estimates to beused in the CSI report to the base station according to the receivedindication; and transmitting the CSI report to the base station, the CSIreport including the determined CSI estimates.
 2. The method accordingto claim 1, wherein the message is a Radio Resource Control, RRC,configuration message.
 3. A User Equipment, UE, for determining ChannelState Information, CSI, estimates to be transmitted in a CSI report to abase station in a radio communications network, the UE comprising one ormore processors whereby the UE is configured to: receive a messagecomprising an indication to use CSI estimates that are based on a CSImeasurement at only a single time instant on a Channel State InformationReference Symbols, CSI-RS, resource configured for the UE, and that arefurther based on a CSI measurement on a Channel State InformationInterference Measurement, CSI-IM, resource at only the single timeinstant; discard existing CSI estimates when there is a change in atleast one transmission condition for the UE; determine the CSI estimatesto be used in the CSI report to the base station according to thereceived indication; and transmit the CSI report to the base station,the CSI report including the determined CSI estimates.
 4. The UEaccording to claim 3, wherein the message is a Radio Resource Control,RRC, configuration message.
 5. A method performed by a base station forcontrolling Channel State Information, CSI, estimates transmitted by aUser Equipment, UE, in CSI reports to the base station in a radiocommunications network, the method comprising: determining that the CSIestimates from the UE are no longer valid due to a change in at leastone transmission condition; transmitting, to the UE, a messagecomprising an indication to use CSI estimates that are based on a CSImeasurement at only a single time instant on a Channel State InformationReference Symbols, CSI-RS, resource configured for the UE, and that arefurther based on a CSI measurement on a Channel State InformationInterference Measurement, CSI-IM, resource at only the single timeinstant; and receiving a CSI report from the UE, the CSI reportincluding CSI estimates in accordance with the indication to use the CSIestimates that are based on the CSI measurement at only the single timeinstant on the CSI-RS resource configured for the UE and that arefurther based on the CSI measurement on the CSI-IM resource at only thesingle time instant.
 6. The method according to claim 5, wherein thebase station is configured for beamforming transmissions to the UE inthe radio communications network, and wherein the change in the at leastone transmission condition is a change in a transmitting beam used inbeamforming the transmissions to the UE.
 7. The method according toclaim 5, wherein the change in the at least one transmission conditionis a change in a traffic situation in a cell in which the UE is located.8. The method according to claim 5, wherein the message is a RadioResource Control, RRC, configuration message.
 9. A base station forcontrolling Channel State Information, CSI, estimates transmitted by aUser Equipment, UE, in a CSI report to the base station in a radiocommunications network, the base station comprising: at least oneprocessor; memory storing executable computer programs, whereby whenexecuted by the at least one processor, the base station is configuredto: determine that the CSI estimates from the UE are no longer valid dueto a change in at least one transmission condition; and transmit, to theUE, a message comprising an indication to use CSI estimates that arebased on a CSI measurement at only a single time instant on a ChannelState Information Reference Symbols, CSI-RS, resource configured for theUE, and that are further based on a CSI measurement on a Channel StateInformation Interference Measurement, CSI-IM, resource at only thesingle time instant.
 10. The base station according to claim 9, whereinthe base station is configured for beamforming transmissions to the UEin the radio communications network, and wherein the change in the atleast one transmission condition is a change in a transmitting beam usedin beamforming the transmissions to the UE.
 11. The base stationaccording to claim 9, wherein the change in the at least onetransmission condition is a change in a traffic situation in a cell inwhich the UE is located.
 12. The base station according to claim 9,wherein the message is a Radio Resource Control, RRC, configurationmessage.
 13. A non-transitory computer program product, comprisinginstructions which, when executed on at least one processor, cause theat least one processor to, in order to determine Channel StateInformation, CSI, estimates to be transmitted in a CSI report from aUser Equipment, UE, to a base station in a radio communications network:receive a message comprising an indication to use CSI estimates that arebased on a CSI measurement at only a single time instant on a ChannelState Information Reference Symbols, CSI-RS, resource configured for theUE, and that are further based on a CSI measurement on a Channel StateInformation Interference Measurement, CSI-IM, resource at only thesingle time instant; discard existing CSI estimates when there is achange in at least one transmission condition for the UE; determine theCSI estimates to be used in the CSI report to the base station accordingto the received indication; and transmit the CSI report to the basestation, the CSI report including the determined CSI estimates.
 14. Anon-transitory computer program product, comprising instructions which,when executed on at least one processor, cause the at least oneprocessor to, in order to control Channel State Information, CSI,estimates transmitted by a User Equipment, UE, in a CSI report to a basestation in a radio communications network: determine that the CSIestimates from the UE are no longer valid due to a change in at leastone transmission condition; transmit, to the UE, a message comprising anindication to use CSI estimates that are based on a CSI measurement atonly a single time instant on a Channel State Information ReferenceSymbols, CSI-RS, resource configured for the UE, and that are furtherbased on a CSI measurement on a Channel State Information InterferenceMeasurement, CSI-IM, resource at only the single time instant; andreceive the CSI report from the UE, the CSI report including CSIestimates in accordance with the indication to use the CSI estimatesthat are based on the CSI measurement at only the single time instant onthe CSI-RS resource configured for the UE and that are further based onthe CSI measurement on the CSI-IM resource at only the single timeinstant.